The function of the butterfly needle is draw blood samples from wrist, hand and foot , its benefits really appear when the veins are too deep or when uncooperative patients keep moving or is anxious during blood drawn

Butterfly needles, also known as winged infusion sets, are a very common
needle style used to collect blood during a venipuncture. The butterfly
needle consists of the stainless steel collection needle fitted with
flexible "wings," which the phlebotomist uses to grip the needle, and a
valve that attaches to a tube, through which blood drawn flows into a
collection tube. Butterfly needles are popular because of their
ease-of-use, and their size makes them an optimal choice for drawing
blood from children or geriatric patients.